fix(context_management): move a client compaction summary into the system prompt when clearing runs before compact

litellm/llms/anthropic/messages/adapters/handler.py

@@ -163,17 +163,17 @@ async def prepare_context_managed_request(
     )
 
     # Skip the client-history pre-processing when a ``compact_20260112``
-    # polyfill spec will run: that editor already slices around any client-sent
+    # polyfill edit runs first: that editor already slices around any client-sent
     # compaction block in its Phase A (and uses the full post-compaction tail
     # for its token-threshold check). Pre-collapsing to just the latest user
     # question here would starve the polyfill of conversation context and
     # silently drop intermediate turns.
-    polyfill_will_run: Final = _polyfill_will_run(
+    compact_runs_first: Final = _compact_runs_first(
         context_management_spec=context_management_spec,
         additional_drop_params=additional_drop_params,
     )
 
-    if polyfill_will_run:
+    if compact_runs_first:
         history_result: PolyfillResult | None = None
         working_messages: _AnthropicMessages = messages
         working_system: _AnthropicSystem = system
@@ -211,7 +211,7 @@ async def prepare_context_managed_request(
     # ``_run_polyfill_if_enabled``), apply the slice-only fallback now so
     # Anthropic-specific ``compaction`` content blocks don't leak through
     # to non-Anthropic backends that would reject them.
-    if polyfill_will_run and history_result is None:
+    if compact_runs_first and history_result is None:
         history_result = apply_client_compaction_block_history(
             messages=messages,
             system=system,
@@ -219,18 +219,18 @@ async def prepare_context_managed_request(
     return history_result
 
 
-def _polyfill_will_run(
+def _compact_runs_first(
     *,
     context_management_spec: _ContextManagementSpec,
     additional_drop_params: list[str] | None,
 ) -> bool:
-    """Return True when ``compact_20260112`` will run via the polyfill dispatcher.
+    """Return True when ``compact_20260112`` is the first edit the polyfill dispatcher runs.
 
     Mirrors the gating in ``_run_polyfill_if_enabled``: an empty spec or an
     explicit ``context_management`` entry in ``additional_drop_params``
-    short-circuits the polyfill. The pre-processing skip only applies when the
-    dispatcher will actually invoke ``apply_compact_20260112`` (which has its
-    own compaction-block slicing).
+    short-circuits the polyfill. The pre-processing skip only applies when
+    ``apply_compact_20260112`` (which has its own compaction-block slicing)
+    sees the messages before any other editor does.
     """
     edits: Final = _normalize_spec_edits(
         context_management_spec=context_management_spec,
@@ -243,7 +243,7 @@ def _polyfill_will_run(
         COMPACT_EDIT_TYPE,
     )
 
-    return any(edit.get("type") == COMPACT_EDIT_TYPE for edit in edits)
+    return bool(edits) and edits[0].get("type") == COMPACT_EDIT_TYPE
 
 
 def _spec_has_non_compact_edits(

tests/unit/llms/anthropic/messages/context_management/test_clear_tool_uses.py

@@ -724,8 +724,9 @@ def test_input_tokens_trigger_counts_the_system_prompt(system: str | list[dict[s
     assert with_system["cleared_input_tokens"] == met_without_system["cleared_input_tokens"] > 0
 
 
-async def test_input_tokens_trigger_counts_a_client_compaction_summary() -> None:
-    """A client compaction summary moves into the system prompt, so the trigger counts it too."""
+@pytest.mark.parametrize("compact_position", [None, "after", "before"], ids=["alone", "before_compact", "after_compact"])
+async def test_input_tokens_trigger_counts_a_client_compaction_summary(compact_position: str | None) -> None:
+    """A client compaction summary moves into the system prompt, so the trigger counts it too, in any edit order."""
     tail: Final = _make_history(n_pairs=3)
     edit_spec: Final = {
         "type": "clear_tool_uses_20250919",
@@ -733,6 +734,10 @@ async def test_input_tokens_trigger_counts_a_client_compaction_summary() -> None
         "keep": {"type": "tool_uses", "value": 1},
     }
     compacted_turn: Final = {"role": "assistant", "content": [{"type": "compaction", "content": "Earlier work. " * 400}]}
+    compact_spec: Final = {"type": "compact_20260112", "trigger": {"type": "input_tokens", "value": 50_000}}
+    edits: Final = {None: [edit_spec], "after": [edit_spec, compact_spec], "before": [compact_spec, edit_spec]}[
+        compact_position
+    ]
 
     async def prepare(messages: list[dict[str, object]]) -> PolyfillResult | None:
         return await prepare_context_managed_request(
@@ -740,18 +745,21 @@ async def test_input_tokens_trigger_counts_a_client_compaction_summary() -> None
             messages=messages,
             tools=None,
             system=None,
-            context_management_spec={"edits": [edit_spec]},
+            context_management_spec={"edits": edits},
             litellm_metadata=None,
             additional_drop_params=None,
             llm_router=None,
         )
 
+    def cleared(result: PolyfillResult | None) -> list[object]:
+        applied: Final = result.applied_edits if result is not None else []
+        return [edit.get("cleared_tool_uses") for edit in applied if edit.get("type") == "clear_tool_uses_20250919"]
+
     without_summary: Final = await prepare(deepcopy(tail))
     with_summary: Final = await prepare([compacted_turn, *deepcopy(tail)])
 
-    assert without_summary is None or not without_summary.applied_edits
-    assert with_summary is not None
-    assert [edit.get("cleared_tool_uses") for edit in with_summary.applied_edits] == [2]
+    assert cleared(without_summary) == []
+    assert cleared(with_summary) == [2]
 
 
 @pytest.mark.parametrize(("clear_tool_inputs", "triggers"), [(False, False), (True, True)])